Because you don’t have to, right? Escalators are magic stairs that walk themselves. You can do nothing and still move. Great, right? But should you stand still on an escalator just because it’s moving you? What if it moves you more slowly than your legs?
What if you walked up escalators? Then you would be moved by your legs AND the escalator, and get where you’re going even faster. And you’re going places, right? Or are you just standing there?
At the airport, I often see people without heavy luggage standing on the people movers (the flat conveyor belt walkways), which move them forward more slowly than their own feet. Why? Don’t they have somewhere better to be? The path of least resistance sometimes adds resistance. Resist the path of least resistance.
Move yourself forward.